The present invention relates generally to release valves, and more particularly to release valves and methods for venting cooling systems.
Fuel cells electrochemically convert reactants, for example, a fuel and an oxidant, to electricity. Unlike batteries, which typically contain a set amount of chemicals for generating electricity and which stop delivering electricity once the chemicals are consumed, fuel cells can deliver electricity continuously as long as the fuel cells receive a fuel and an oxidant.
A Proton Exchange Membrane (hereinafter xe2x80x9cPEMxe2x80x9d) fuel cell converts the chemical energy of reactants such as hydrogen and oxidants such as air/oxygen directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (i.e., H+ions) from the xe2x80x9canodexe2x80x9d side of a fuel cell to the xe2x80x9ccathodexe2x80x9d side of the fuel cell while preventing passage therethrough of the reactants (e.g., hydrogen and air/oxygen).
Fuel cell systems typically include one or more closed loop cooling systems through which a coolant liquid circulates for removing heat from the fuel cell via a heat exchanger. A problem with such cooling systems is the accumulation of gas in the cooling system which adversely affects the coolant circulation and the proper functioning of heat exchangers. Gases, mainly air, can be drawn into the cooling system from the outside or from a fuel cell cabinet (main enclosure around the fuel cell) due to local negative pressures during normal operation or during a coolant drain process when the system is temporarily shut down. In order to ensure proper and efficient operation, gas contained in the cooling system during startup and during normal operation needs to be removed. One method for removing gas contained in the cooling system is to use a bleed valve.
There is a need for further improvements in venting gas from fuel cell cooling systems.
The present invention provides, in a first aspect, a release valve having a housing comprising a passageway extending therethrough and defining an inlet and an outlet, and a membrane extending across the passageway between the inlet and the outlet. The membrane is operable to permit passage through the passageway of gas at a first pressure, inhibit passage through the passageway of liquid at the first pressure, and permit passage of liquid at a second pressure greater than the first pressure.
The present invention provides, in a second aspect, a portion of a system through which a fluid is flowable in which the portion of the system includes a conduit having an outer surface and an inner surface defining a passageway through which the fluid is flowable and an opening extending through the conduit from the outer surface to the inner surface. A membrane extends across the opening and the membrane is operable to permit passage through the passageway of gas at a first pressure, inhibit passage through the passageway of liquid at the first pressure, and permit passage of liquid at a second pressure greater than the first pressure.
The present invention provides, in a third aspect, a cooling system through which a coolant is flowable. The cooling system includes a conduit, and a release valve having a housing comprising a passageway extending therethrough and defining an inlet and an outlet. The outlet is operably connected to the conduit and in communication with the coolant. A membrane extends across the passageway between the inlet and the outlet. The membrane is operable to permit passage through the passageway of gas at a first pressure, inhibit passage through the passageway of liquid at the first pressure, and permit passage of liquid at a second pressure greater than the first pressure.
The present invention provides, in a fourth aspect, a fuel cell system having a fuel cell, a cooling system for cooling the fuel cell, and a releases valve or portion of the cooling system, as described above, operably connected to the cooling system.
The present invention provides, in a fifth aspect, a method for venting a system through which a fluid is flowable. The method includes providing a membrane across an opening to the system. The membrane is operable to permit passage of gas at a first pressure and inhibit passage of liquid at the first pressure.
The present invention provides, in a sixth aspect, a method for relieving a predetermined pressure in a system through which a gas and a liquid are flowable. The method includes selecting a membrane operable to permit passage of gas at a first pressure, inhibit passage of liquid at the first pressure, and permit passage of liquid at the predetermined pressure. The membrane is provided across an opening to the system.